Technical Field
The present invention relates to photovoltaic devices, and more particularly to formation methods and devices using absorber layers comprised of a chalcogenide compound having an aluminum-doped zinc oxysulfide emitter.
Description of the Related Art
Conventional solar cell stacks may employ Cu—Zn—Sn—S/Se (CZTSSe or CZTS) as a p-doped absorber layer. The p-CZTS is usually formed on a molybdenum (Mo) coated glass substrate. An n-type layer includes n-CdS on the CZTS layer and often includes a zinc oxide (ZnO) intrinsic layer formed thereon and with an indium tin oxide (ITO) contact. CdS has been used as the n-type layer to form a p-n junction since electron affinity of the CdS matched that of CZTS. A typical electron concentration in CdS is less than 5×1016 cm−3. This is a low concentration that limits the effectiveness of the photovoltaic cell. For example, the low concentration contributes to a substantially reduced built-in potential in the CdS/CZTS junction. In addition, open circuit voltage (Voc) is substantially reduced as well. The low Voc is suspected to be due at least to high interface recombination and possible Fermi level pinning at the interface.